Evolution / Genetics / Biology

Oldest star chart in Nara burial mound may have been retraced

Some of the constellations on what is believed to be the world's oldest surviving star map found inside an ancient burial mound in this western village show signs of redrawn sketch lines, indicating they had been retraced.

Archaeologists have found that the shapes and locations of the constellations were likely transferred onto the ceiling of the Kitora burial mound’s cramped stone chamber by tracing over an original chart.

It remains a mystery, however, why artists of the Asuka Period (late sixth century to early eighth century) had to redraw their initial sketch.

“The star chart was likely drawn by more than one artist,” said Takashi Kitamura, an archaeology professor with Hannan University. “Perhaps a foreman, after inspecting a sketch done by young artists, had it redrawn boldly in favor of more emotion and sensibility.”

The Nara National Research Institute for Cultural Properties has been studying how the artifact was drawn. It was discovered inside the Kitora burial mound, a government-designated “special historic site” that dates from the turn of the seventh century to the eighth century.

The star chart contains four circles drawn on stucco applied on ceiling stones inside the stone chamber: three large concentric circles and a fourth one offset toward the northwest. Glued inside those circles are more than 350 pieces of gold leaf, which are connected with red lines to represent at least 74 constellations.

The NNRICP has been conducting a detailed study of the star chart since 2014. Tomohiro Wakasugi, a researcher with the institute, has attempted to reconstruct the drawing process through replication experiments and other means.

What he assumes is as follows: first, the principle of compasses was used to draw the four big circles. Second, a likeness of carbon paper called “nenshi,” or “washi” paper with charcoal, red ocher or other pigments applied on the back side, was held together with an original chart and against the stucco, whereupon the chart was traced over from above to draw a sketch of constellations.

Third, pieces of gold leaf were glued in reference to the sketch lines and the original chart. Finally, red lines were drawn to link the gold leaf pieces together to finish the images of the constellations.

Washi paper was so precious during the Asuka Period that it was seldom used except when important documents, such as Buddhist scriptures and laws, were transcribed. Scholars assume that the star map was drawn at times by applying colorants directly on the back of the original chart to transfer the image, and also by holding the nenshi beneath the original chart and tracing over the image from above.

In the meantime, traces of likely redrawn sketch lines have been found in some of the constellations, wherein, for example, initial sketch lines are somewhat smaller than the red lines or are located off the red lines.

It remains unknown why the artists redrew the initial sketches of the constellations, whose images they had transferred by tracing over the original chart.

Many scholars, many hypotheses

In addressing this mystery, Wakasugi focuses attention on the work environment in which the star map was drawn.

The star chart was found on the ceiling of a cramped stone chamber, which measured only 1.2 meters tall and 1 meter wide. Many of the gold leaf pieces are only about 6 millimeters across, and the red lines connecting stars are only about 1 mm to 4 centimeters long.

“The artists had to remain face up while doing delicate work,” Wakasugi said. “The constellations are small, each measuring at most 5 cm, so the artists may have made mistakes.”

Kazuhiko Miyajima, a former Doshisha University professor who specializes in the history of astronomy in East Asia, thinks otherwise.

He pointed out that up to 280 or so constellations of 1,400 or so stars were drawn in serious star charts done in China. Drawing a multitude of stars on the ceiling of the small stone chamber would have ended up in tiny constellations jostling each other.

“Perhaps the artists reduced the number of stars and enlarged the constellations to fill the gaps so they would look better,” Miyajima said.